1. Field of the Invention
The present invention relates to an image generating apparatus, and more particularly, it relates to an image generating apparatus comprising a print head.
2. Description of the Background Art
A thermal printer (thermal transfer printer) is generally known as an image generating apparatus performing printing by pressing a print head against a platen provided in the form of a roll or the like. For example, Japanese Patent Laying-Open No. 6-122246 (1994) discloses such a thermal printer (thermal transfer printer).
The aforementioned Japanese Patent Laying-Open No. 6-122246 discloses a thermal printer pressing a print head against a platen roller by urging the printing head portion downward with a spring.
However, the conventional thermal printer disclosed in the aforementioned Japanese Patent Laying-Open No. 6-122246 is provided with no mechanical portion for automatically separating the print head from the platen roller, and hence it is disadvantageously necessary to manually lift up the print head, in order to separate the same from the platen roller.
In this regard, a print head printer provided with a mechanical portion for automatically separating a print head from a printer is proposed in general, as disclosed in Japanese Patent Laying-Open No. 5-309905 (1993), Japanese Patent Laying-Open No. 6-15852 (1994), Japanese Patent Laying-Open No. 6-191066 (1994) or Japanese Patent Laying-Open No. 9-188027 (1997), for example.
The aforementioned Japanese Patent Laying-Open No. 5-309905 discloses a print head, pressed against a platen with urging force of a spring, provided with a mechanical portion (head portion retraction means) formed by a gear wheel, a follower plate and an arm for moving the print head oppositely to the platen against the urging force of the spring.
Each of the aforementioned Japanese Patent Laying-Open No. 6-15852, Japanese Patent Laying-Open No. 6-191066 and Japanese Patent Laying-Open No. 9-188027 discloses a thermal printer, having a print head mounted on an arm synchronously rotating with a cam, capable of pressing and separating the print head against and from a platen roller by rotating the cam thereby rotating the arm. In this thermal printer, coupling arms coupling a support shaft rotatably supporting the print head and the print head with each other are provided on both ends of the print head for rotating the print head about the support shaft by engaging the coupling arms with the arm synchronously rotating with the cam.
In the conventional thermal printer disclosed in the aforementioned Japanese Patent Laying-Open No. 5-309905, however, the number of components is disadvantageously increased due to the mechanical portion (head portion retraction means) formed by the gear wheel, the follower plate and the arm separately provided for moving the print head oppositely to the platen in order to separate the print head from the platen.
In the conventional thermal printer having the print head mounted on the arm synchronously rotating with the cam disclosed in each of the aforementioned Japanese Patent Laying-Open No. 6-15852, Japanese Patent Laying-Open No. 6-191066 and Japanese Patent Laying-Open No. 9-188027, the arm presses only one of the coupling arms of the print head and applies pressing force to only the corresponding end of the print head if the thermal printer has only a single cam since the arm engaging with the cam engages with the coupling arms, and hence the print head cannot be uniformly pressed against the platen roller. In order to uniformly press the print head against the platen roller, therefore, two cams must be provided on both ends of the print head for pressing both ends of a coupling portion of the print head. More specifically, the cams must be arranged on both ends of the print head, and arms synchronously rotating with the cams must also be provided on both ends of the print head. Consequently, the number of components is disadvantageously increased in the conventional thermal printer disclosed in each of the aforementioned Japanese Patent Laying-Open No. 6-15852, Japanese Patent Laying-Open No. 6-191066 and Japanese Patent Laying-Open No. 9-188027, although the print head can be automatically separated from the platen roller. Further, the size of the thermal printer is disadvantageously increased due to the cams arranged on both ends of the print head.